177 research outputs found
Using long-term millisecond pulsar timing to obtain physical characteristics of the bulge globular cluster Terzan 5
Over the past decade the discovery of three unique stellar populations and a
large number of confirmed pulsars within the globular cluster Terzan 5 has
raised questions over its classification. Using the long-term radio pulsar
timing of 36 millisecond pulsars in the cluster core, we provide new
measurements of key physical properties of the system. As Terzan 5 is located
within the galactic bulge, stellar crowding and reddening make optical and near
infrared observations difficult. Pulsar accelerations, however, allow us to
study the intrinsic characteristics of the cluster independent of reddening and
stellar crowding and probe the mass density profile without needing to quantify
the mass to light ratio. Relating the spin and orbital periods of each pulsar
to the acceleration predicted by a King model, we find a core density of
10 M pc, a core radius of 0.16 pc, a pulsar
density profile , and a total mass of M(1.0 pc)10 M assuming a cluster
distance of 5.9 kpc. Using this information we argue against Terzan 5 being a
disrupted dwarf galaxy and discuss the possibility of Terzan 5 being a fragment
of the Milky Way's proto-bulge. We also discuss whether low-mass pulsars were
formed via electron capture supernovae or exist in a core full of heavy white
dwarfs and hard binaries. Finally we provide an upper limit for the mass of a
possible black hole at the core of the cluster of 3.010 M.Comment: 27 pages, 20 figures, 5 tables, thesis research, accepte
On the Mass and Inclination of the PSR J2019+2425 Binary System
We report on nine years of timing observations of PSR J2019+2425, a
millisecond pulsar in a wide 76.5 day orbit with a white dwarf. We measure a
significant change over time of the projected semi-major axis of the orbit,
x-dot/x=(1.3+-0.2)x10^-15 s^-1, where x=(a sin i)/c. We attribute this to the
proper motion of the binary. This constrains the inclination angle to i<72
degrees, with a median likelihood value of 63 degrees. A similar limit on
inclination angle arises from the lack of a detectable Shapiro delay signal.
These limits on inclination angle, combined with a model of the evolution of
the system, imply that the neutron star mass is at most 1.51 solar masses; the
median likelihood value is 1.33 solar masses. In addition to these timing
results, we present a polarization profile of this source. Fits of the linear
polarization position angle to the rotating vector model indicate the magnetic
axis is close to alignment with the rotation axis, alpha<30 degrees.Comment: Accepted by Ap
Probing the Masses of the PSR J0621+1002 Binary System Through Relativistic Apsidal Motion
Orbital, spin and astrometric parameters of the millisecond pulsar PSR
J0621+1002 have been determined through six years of timing observations at
three radio telescopes. The chief result is a measurement of the rate of
periastron advance, omega_dot = 0.0116 +/- 0.0008 deg/yr. Interpreted as a
general relativistic effect, this implies the sum of the pulsar mass, m_1, and
the companion mass, m_2, to be M = m_1 + m_2 = 2.81 +/- 0.30 msun. The
Keplerian parameters rule out certain combinations of m_1 and m_2, as does the
non-detection of Shapiro delay in the pulse arrival times. These constraints,
together with the assumption that the companion is a white dwarf, lead to the
68% confidence maximum likelihood values of m_1 = 1.70(+0.32 -0.29) msun and
m_2 =0.97(+0.27 - 0.15) msun and to the 95% confidence maximum likelihood
values of m_1 = 1.70(+0.59 -0.63) msun and m_2 = 0.97(+0.43 -0.24) msun. The
other major finding is that the pulsar experiences dramatic variability in its
dispersion measure (DM), with gradients as steep as 0.013 pc cm^{-3} / yr. A
structure function analysis of the DM variations uncovers spatial fluctuations
in the interstellar electron density that cannot be fit to a single power law,
unlike the Kolmogorov turbulent spectrum that has been seen in the direction of
other pulsars. Other results from the timing analysis include the first
measurements of the pulsar's proper motion, mu = 3.5 +/- 0.3 mas / yr, and of
its spin-down rate, dP/dt = 4.7 x 10^{-20}, which, when corrected for kinematic
biases and combined with the pulse period, P = 28.8 ms, gives a characteristic
age of 1.1 x 10^{10} yr and a surface magnetic field strength of 1.2 x 10^{9}
G.Comment: Accepted by ApJ, 10 pages, 5 figure
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